The purpose of this research project is to understand at the morphological, cellular and biochemical levels various aspects of normal and abnormal embryonic development, especially relating to craniofacial development. Glucocorticoids are teratogenic in vivo, and our results using whole rodent embryo culture demonstrate they exert a direct effect on the embryo; day 8 embryos cultured fo 48 hrs develop heart and neural tube malformations whereas day 10 embryos develop cleft lip in culture after a 48 hr exposure to triamcinolone acetonide. Cultured day 10 mouse embryos become responsive to epidermal growth factor (EGF) after 48 hrs in culture, during which time the initial stages of secondary palate formation are occurring; future studies will ascertain the effect of other growth factors and hormones. Our results indicate that maternal EGF does not cross the mouse placenta although an embryonic form of EFG appears in the conceptus on day 12 of gestation; future work will determine the site(s) of synthesis of this EGF within the embryo. A cell culture system has been developed in order to examine growth and differentiation of isolated embryonic palatal epithelial cells and EGF is an absolute requirement; the effects of EGF are enhanced in the presence of cyclic AMP. The dioxin TCDD appears to induce cleft palate by altering the differentiation of the medial palatal epithelial cells. Glucocorticoids exert their cleft palate inducing effects by inhibiting palatal mesenchymal cell proliferation; immunocytochemical studies have localized glucocorticoids receptors mainly to the palatal mesenchyme. In palatal mesenchyme cell culture, one of the major effects produced by glucocorticoids associated with growth inhibition is an alteration in the turnover of plasma membrane phosphatidylinositol; future studies will examine the effect in greater detail. An established line of human embryonic palatal mesenchymal cells, along with a liver-derived metabolic activating system, has been used to develop a short-term growth-inhibition screening test for potential teratogens.